Each of various kinds of chromatography has been used as a method of separating a desired substance in a sample. A known example of such the chromatography is supercritical fluid chromatography using a supercritical fluid as a mobile phase. Since the supercritical fluid chromatography uses a fluid, which is referred to as a supercritical fluid and has a greater variety of properties than that of a general solvent, as a mobile phase, investigation has been conducted into the utilization of supercritical fluid chromatography for the separation, analysis, purification, and the like of various substances that have been considered to be difficult to separate.
A technique has been known as the method of substance separation by supercritical fluid chromatography, which involves: delivering a supercritical fluid supplied from a bomb by using a pump; injecting a sample into the supercritical fluid; passing the supercritical fluid into which the sample has been injected through a column; reducing the pressure of the supercritical fluid that has been passed through the column to precipitate a solute; dividing the precipitated solute and the supercritical fluid; and delivering the divided supercritical fluid to the pump to recycle the supercritical fluid (see, for example, Japanese Patent Laid-Open Publication 05-307026).
By the way, a mobile phase obtained by mixing a supercritical fluid and a solvent is used in supercritical fluid chromatography depending on the kind of a solute and the kind of a filler in some cases. The above technique does not show the use of such mobile phase, so the recycling of the supercritical fluid upon use of such mobile phase is susceptible to investigation.